Processes of producing unsaturated fatty acids from olefins through unsaturated aldehyde correspond to representative catalytic vapor phase oxidation.
In partial oxidation of olefins, molybdenum oxides, bismuth oxides, and transition metal oxides are used to prepare catalysts. As representative processes, there are a process of preparing (meth)acrylic acid through (meth)acrolein by oxidizing propylene or isobutylene, a process of preparing phthalic anhydride by oxidizing naphthalene or ortho-xylene, or a process of preparing maleic anhydride by partially oxidizing benzene, butylene or butadiene.
In the first step, oxygen, propylene or isobutylene is oxidized by dilute inactive gas, vapor and a predetermined amount of catalyst, mainly preparing (meth)acrolein. In the second step, the (meth)acrolein is oxidized by oxygen, dilute inactive gas, vapor and a predetermined amount of catalyst, thereby preparing the (meth)acrylic acid. Devices performing such processes may be provided such that both steps are performed in one device or in respective devices.
The (meth)acrylic acid is mainly used to prepare (meth)acrylate used as coating materials such as paint, textile auxiliaries, paper, etc. by reacting with alcohol. In addition, high-purity (meth)acrylic acid is used as a raw material of high-hygroscopicity resins, demand for which is rapidly increasing.
In general, metal oxide catalysts are prepared through co-precipitation, hydrothermal synthesis, sol-gel synthesis, physical mixing, etc. The metal oxide catalysts are precipitated into a polyanion, metal oxide or metal hydroxylate form in the reaction processes, and physical characteristics and morphologies of the precipitates depend upon the pH or concentration of an aqueous solution, reaction temperature or aging time, thereby affecting a physical state, particle sizes and crystalline structure.
Examples of ligands that are bonded to oxoanions and transition metal precursors used in catalysts for preparing unsaturated fatty acids include —NH4, —NH2, —NOx, —Cl, —F, —N, —OH (hydroxyl), —SOx, —CO, —COO, —CnHmOx, alkoxide (O-metal), etc. Such ligands may be utilized as an ingredient for controlling catalytic activities by changing physicochemical characteristics of catalysts according to proper control methods as an essential ingredient upon dissolution or purification of metal oxides.
Japanese Patent No. 4295521 as a related art introduces a catalyst preparation technology wherein a catalyst is prepared by powder-coating and firing a bulk carrier. This technology produces an acrylic acid catalyst wherein a reduction ratio of a dry matter is 5 to 40% by mass at a 300° C. atmosphere as a catalyst-drying temperature. Such a preparation method has a relatively high drying temperature and thus change in a catalyst structure is caused, thereby disadvantageously affecting catalytic performance and thus tending to exhibit a low transition rate.
In addition, Korean Patent No. 10-0746971 introduces a catalyst wherein the catalyst includes molybdenum and vanadium, the content of catalyst poison measured by ion chromatography is 10 to 100 ppb, at least one volatile catalyst poison ingredient is additionally included, and acrylic acid is generated through vapor-phase contact oxidation of oxygen molecules and acrolein, and an acrylic acid preparation method including performing catalytic vapor phase oxidation of oxygen molecules and acrolein using the catalyst.
The catalyst is prepared through addition of aqueous ammonia as a catalyst poison ingredient, thereby lowering hot spot temperature and suppressing reaction efficiency decrease accompanied with degradation. Accordingly, an acrolein transition rate may be stably maintained for a long time. However, if a reducing material such as ammonia is present in a catalyst, the material functions as a catalyst poison, thus greatly increasing reaction temperature and activating the catalyst after extended use. Accordingly, a reducing material may be used as a catalyst poison for controlling catalytic activity, but there are considerable difficulties in performing quantitative control during a catalyst preparation process.
In addition, although inorganic salts present in catalyst precursors should be treated such that the amount thereof is decreased during a catalyst preparation process, a reducing material removal process is additionally required due to further addition of inorganic salts. Accordingly, there is a need for technology being simple and having superior reproducibility, which may sublimate, during catalyst calcination, ligands included in a catalyst.